1. Field of the Invention
The present invention relates to a zoom lens, which is suitable as an image pickup optical system used in image pickup apparatuses such as video cameras, monitoring cameras, digital still cameras, broadcasting cameras, and silver halide photography cameras.
2. Description of the Related Art
An image pickup optical system used for image pickup apparatuses such as video cameras, monitoring cameras, and digital still cameras using a solid-state image pickup element is required to be a high-zoom-ratio wide-angle zoom lens for which the entire system is compact and, in addition, to be a zoom lens having a high optical performance over the entire zoom range. Furthermore, a reduction in the power consumption of a drive source required for zooming, prevention of imperceptible shaking of images, and fixation of a first lens unit that is large and heavy in order to enhance the strength of a lens barrel at the time of zooming are required.
A positive-lead-type five-unit zoom lens including a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, a fourth lens unit having a negative refractive power, and a fifth lens unit having a positive refractive power in order from an object side to an image side is known. Then, a rear-focus-type five-unit zoom lens configured to perform zooming by moving the second lens unit and the third lens unit, correct an image plane variation in association with the zooming and perform focusing by moving the fifth lens unit is known.
U.S. Pat. No. 7,253,961 discloses a zoom lens having a high optical performance over an entire zoom range at a high zoom ratio.
U.S. Pat. No. 5,388,004 discloses a zoom lens for which the entire system is compact even though the shooting angle of view at a wide-angle end is as wide as 60 degrees or more, and the zoom ratio is as high as twelve times.
U.S. Pat. No. 7,894,135 discloses a zoom lens having a high optical performance in which a variation in aberration at the time of correcting the image shaking is desirably corrected while achieving a reduction in the size and weight of the correction lens unit for correcting the image shaking.
However, when refractive powers of the respective lens surfaces are increased for achieving a reduction in size, the occurrence of axial chromatic aberration, magnification chromatic aberration, and coma aberration is increased at a telephoto end, and correction of such aberrations tends to be difficult.
The five-unit zoom lenses as described above are of a zoom type with which it is relatively easy to obtain a desirable optical performance while achieving a reduction in the size of the entire lens system with a high zoom ratio and a wide angle of view. However, in order to obtain the characteristics as described above, it is important to set the refractive powers of the respective lens units or conditions for movement in association with the zooming operations of the respective lens units appropriately.
In particular, it is important to set the parameters of movement at the time of zooming of the second and third zoom lens unit. If the conditions of movement at the time of zooming of the second and third lens units are not set appropriately, it is difficult to achieve a reduction in the size of the entire system and obtain a high optical performance at a high zoom ratio and a wide angle of view over the entire zoom range.